The production of structures on supports or substrates requires a high degree of accuracy, particularly when, as in the case of ink printheads, the channels and/or the webs lying between them are located close together, in order to obtain the smallest possible structural size. Present printing technology requires a print resolution in excess of about 180 dots per inch, and possibly about 360 dots per inch. A ink jet printhead for use in such a printer must have a channel placement accuracy equal or better than the dot pitch, and if used in a single pass over the recording medium, must have a pitch equal to the intended dot pitch.
The prior art teaches the production of structures by the silk screen technique or by etching of a surface layer, in order to obtain the desired structure. The high degree of precision required is, however, not always assured thereby, particularly when a high flank or wall steepness of the applied structures is important in order to obtain a resulting printhead capable of high resolution printing. Thus, an imprecise production method may result in poor production yield, and/or printheads that clog easily, have inconsistent flow or are otherwise suboptimal.
A photolithographic method is also known for the production of structures on supports. For this purpose, a support is provided with a dry-film resist coating a surface of a substrate, which is selectively exposed to radiation at the places which, after development, are subsequently to form the elevations, i.e. the regions remaining between the ink channels, in the case of ink printheads. Thus, after developing the latent image produced by the irradiation, a relief pattern is formed on the substrate, where the dry film resist, after exposure, is stabilized and is not removed by the development process.
The dry film resist, in unexposed condition, is a tacky composition which is generally covered by a protective foil or covering layer. If such an arrangement is now exposed, parts of the light are deflected, dispersed or reflected by the protective foil so that after the development process, the side walls formed are only approximately perpendicular to the surface of the support, thus reducing the precision of the resulting structure.
An improvement over this method is obtained by omitting the protective foil, since this serves to reduce light dispersion.
Methods of forming ink channels in ink jet printheads by photopolymerizing a photosensitive polymer are disclosed in U.S. Pat. Nos. 4,789,425; Re. 32,572; 4,727,012; 4,698,645; 4,666,823; 4,609,427; 4,509,063; 4,417,251; 4,412,224; and 4,394,670, which are incorporated herein by reference. Such a method is also disclosed in Japanese Laid-open Publication No. 43876/1982, which is incorporated herein by reference.